In an attempt to determine the incidence of the cercarial larvae of trematodes, Semisulcospira snails collected in Judong stream, an endemic area of Paragonimus westermani, in Kyungpook Province, Korea, were examined from 1965 to 1980. The infestation rate for cercariae in the snails was 5.4 per cent, but in 1970 dropped to 4.0 per cent and remained at the same level, 4.2 per cent, in 1975. It then decreased to 3.5 per cent in 1980. Seven species of cercariae, Cercaria incerta(Kobayashi, 1992) Faust, 1924, Cercaria nipponensis(Ando, 1915) Faust, 1924, Cercaria yoshidae(Osafune, 1898) Cort et Nichols, 1920, Centrocestus armatus(Tanabe, 1922) Yamaguti, 1934, Metagonimus species, Notocotylus magniovatus Yamaguti, 1934, and Paragonimus westermani(Kerbert, 1878), and five kinds of undeterminced cercariae were found. Of these, the most freqently emerged cercaria was Metagonimus species, folllowed by Notocotylus magniovatus. The least freqently emerged was Paragonimus westermani, with the rate of 0.04 per cent. The liberation rates in the five kinds of undetermined species varied from 0.04 to 0.15 per cent. In the monthly liberaton rates for cercariae, the highest rate was encountered in May, and decreased in the period from June to November. It then somewhat increased again in December. There was no correlation in the liberation rate for cercariae and length of snails. The results of this study indicate that the infestation of Semisulcospira snails with the cercariae of trematodes has decreased over the fifteen year period from 1965 to 1980.
parasitology-helminth-trematoda ; Semisulcospira sp. ; Paragonimus westermani ; Cercaria incerta ; Cercaria nipponensis ; Cercaria yoshidae ; Centrocestus armatus ; cercaria ; epidemiology

The aim of this study was to conduct a freshwater snail survey in Mae Lao agricultural basin to assess the diversity with a focus on habitat types and their larval trematode infections. Snails were collected and examined in 14 sites of Mae Lao agricultural basin from August 2016 to October 2017. A total of 1,688 snail individuals were collected and classified into 7 families, 8 genera, and 12 species. Snail diversity and habitat types were higher in rice paddies than irrigation canals and streams. The most abundant species was Bithynia siamensis siamensis, representing 54.6% of the sample. Three species of snails act as first intermediate host were found with cercarial infections. They were Filopaludina sumatrensis polygramma, B. s. siamensis, and Melanoides tuberculata. The cercariae were categorized into 7 types; echinostome, monostome, gymnocephalous, virgulate, parapleurolophocercous, pleurolophocercous and megalurous cercariae. Parapleurolophocercous cercariae constituted the most common type of cercariae recovered, contributing 41.2% of all infections in snails. Echinostome metacercariae infections were found in 6 snail species with 7.6% prevalence. In addition, the metacercaria of avian trematode, Thapariella sp. were found in Filopaludina spp. snails and B. funiculata with a prevalence of 0.5%. This is the first report for Thapariella metacercariae in the snail host, B. funiculata, and also confirmed that viviparid and bithyniid snails act as the second intermediate hosts of this trematode. This work will provide new information on the distribution and intermediate host of trematode in this area.
Cercaria ; Ecosystem ; Fresh Water ; Humans ; Metacercariae ; Prevalence ; Rivers ; Snails ; Trematode Infections

The pattern of sensory papillae, chaetotaxy, of the cercaria of Clonorchis sinensis was observed. The chaetotaxy was as follows; 5-6 Ci l, 4-5 Ci 2, 5-6 Ci 3 at lst row, 4 Cii 1, 2 Cii 2, 4 Cii 3, 5-6 Cii 4 at 2nd row, 3-4 Ciii 1, 2-3 Ciii 2 at 3rd row, and 2 Civ 1, 2-3 Civ 2, 2-3 Civ 3, at 4th row, in cephalic region; 2 AiV, l AiD, 2 AiiV, 1 AiiD, 2 AiiiV, 2 AiiiD, 1 AivV, 1 AivD, 1 PiiD, l PiiiD, in ventral(V) and dorsal(D) portions of body. Caudal region revealed 2-2-2-2 formula.
parasitology-helminth-trematoda ; Clonorchis sinensis ; cercaria

The Jinyang Lake is dammed up Nam River, and surrounded by Jinju city and four counties; Jinyang, Sanchong, Hadong, and Sachon in Kyongsang-Nam-Do, Korea. The area around this man-made lake have been known as an endemic focus of clonorchiasis in Korea. The present study was first aimed to know the distribution of freshwater mollusks including medically important snails, and larval trematodes shed from Parafossarulus manchouricus and Semisulcospira libertina. In addtion to above studies, water analyses in each snail habitat were carried out in order to figure out a part of their environmental factors. This malaco-ecological survey was done at the six areas around upper, middle and lower parts of the lake for 4 months, August-November, 1983. Total nine species of freshwater mollusks were collected throughout the study: 4 species of gastropods; Semisulcospira libertina, Cipangopaludina chinensis, Parafossarulus manchouricus and Radix auricularia, and 5 species of bivalves; Unio douglasiae, Anodonta woodiana, Lamprotula gottschei, Corbicula fluminea and Limnoperma lucustris. Out of nine species of freshwater mollusks, three species of gastropods; S. libertina, P. manchouricus and R. auricularia were medically important in terms of the transmission of digenetic trematodes to humans. P. manchouricus and R. auricularia were mainly collected from the shallow ponds and the irrigation channels with the muddy basin, but S. libertina and the bivalves were only collected from the stream of Nam river where the gravels and rocks were dominant. The levels of dissolved oxygen(D.O.) and biochemical oxygen demand (B.O.D.(5)) of the water specimens sampled from the study areas ranged from 6.0 to 9.6 ppm and from 0.4 to 1.6 ppm respectively. As a result, it is considered that water system around the Jinyang Lake might be relatively clean without any heavy pollution of aquatic microorganisms and organic materials during the period of this study. On the other hand, eight metalic constituents from the water samples were also assayed, and all metalic ions detected were remarkably low below the legal criteria. However, calcium ion in the water samples from the habitats of P. manchouricus was considerably higher than others. Infection rates of digenetic trematodes in the snails were 6.9 percent in P. manchouricus and 4.8 poercent in S. libertina, respectively. P. manchouricus snails harboring with the cercariae of Clonorchis sinensis were only 0.14 percent among the snails examined and other trematode cercariae except cercaria of C. sinensis were; furcocercus cercariae, cercaria of Loxogenes liberum type I and II. S. libertina snails parasitized with the cercariae of Metagonimus yokogawai were 1.5 percent out of the snails examined and no cercaria of Paragonimus westermani was found in S. libertina snails in the present study. Digenetic trematode cercariae other then M. yokogawai in S. libertina snails were: Cercaria yoshidae (B type), Cercaria cristata, Cercaria innominatum, Cercaria of Centrocestus formosanus and Cercaria nipponensis.
parasitology-helminth-trematoda ; Clonorchis sinensis ; Loxogenes liberum ; Metagonimus yokogawai ; Centrocestus formosanus ; Cercaria cristata ; Cercaria innominatum ; Cercaria nipponensis ; epidemiology ; Parafossarulus manchouricus ; Semisulcospira libertina ; Radix auricularia

The prevalence of cercarial infection in freshwater snails and their evolutionary trends were studied in Nakhon Nayok province, Thailand. A total of 2,869 individual snails were examined for parasitic infections. The results showed that 12 snail species were found to host larval stages of trematodes with an overall prevalence of 4.7%. The infected specimens included 7 types at the cercarial stage; cercariae, megalurous cercariae, echinostome cercariae, furcocercous cercariae, parapleurolophocercous cercariae, virgulate cercariae, and xiphidiocercariae. Regarding molecular identification, ITS2 sequence data of each larval trematode were analyzed, and a dendrogram was constructed using the neighbor-joining method with 10,000 replicates. The dendrogram was separated into 6 clades (order/family), including Echinostomatida/Echinostomatidae, Echinostomatida/Philophthalmidae, Opisthorchiida/Heterophyidae, Plagiorchiida/Prosthogonimidae, Plagiorchiida/Lecithodendriidae, and Strigeatida/Cyathocotylidae. These findings were used to confirm morphological characteristics and evolutionary trends of each type of cercariae discovered in Nakhon Nayok province. Furthermore, this investigation confirmed that the ITS2 data of cercariae could be used to study on phylogenetic relationships or to determine classification of this species at order and/or family level when possible.
Cercaria* ; Classification ; Fresh Water* ; Humans ; Methods ; Prevalence ; Snails* ; Thailand*

As a part of observation on the suitability as a second intermediate host of Clonorchis sinensis, various infection experiments were tried to Cyprinus carpio nudus. The results obtained were summarized as follows: The cercariae which attempted to contact with Cyprinus carpio nudus in the water were observed under the stereomicroscope. After contact, cercariae began to separate its tails from the bodies at 4 minutes increasingly, and then the number ranged to 80 percent at 13 minutes after the encounter. But very few cercariae could actually invade into the epidermis of the fish. When Cyprinus carpio nudus were exposed to a number of cercariae in the beaker, only a few cercariae could invade through the epidermis. Most of the invaded cercariae were killed before forming the cyst. Also rare encysted cercariae were found to be dead within 48 hours. Cyprinus carpio nudus were reared with Parafossarulus manchouricus shedding numerous cercariae in the indoor aquarium. When observed after 12 days, to determine the susceptibility, no metacercaria was found infected. Cyprinus carpio nudus were reared with Parafossarulus manchouricus shedding numerous cercariae in Kimhae lake for 2 months in summer of 1982, in order to check the natural infection. No metacercaria of Clonorchis sinensis was found from the fish. In the cases of control fish, Pseudorasbora parva, numerous cercariae were inspected on the course of invasion through epidermis of the fish under the stereomicroscope. And many metacercariae were also found from the fish whenever they were kept in beaker, indoor aquarium, or the lake for natural infection. The results suggested that Cyprinus carpio nudus might not be proper intermediate host of Clonorchis sinensis.
parasitology-helminth-trematoda ; Clonorchis sinensis ; Cyprinus carpio nudus ; Parafossarulus manchouricus ; cercaria ; biology

Studies were conducted to determine the ecology of the snail, Parafossarulus manchouricus, the seasonal variation of the snail population, and the infestation rates of these snails with the cercariae of digenetic trematodes, in the snail habitat of river Kumho, in Dongchon of Taegu city, in Kyungpook Province, Korea, from 1975 to 1979. The earliest time the snails were found was early in April every year. At that time the water temperature ranged from 13 to 14 degrees C. The population density of snails ranged from 2 to 8 per square meter. The highest population density of snails was encountered in late June and the water temperature was between 24 and 26 degrees C. The snails disappeared in early and mid-November, when the water temperature dropped to 10-13 degrees C. The average snail population in June was 115.9 per square meter in 1975 but in 1976 dropped abruptly to 30.5 and remained at approximately the same level in 1977. It then decreased at considerably lower rates, with the average of 18.7 in 1978 and 14.5 in 1979. The snails collected in the habitat were examined for the presence of cercariae of digenetic trematodes. Of these, four species, Clonorchis sinensis, Cyathocotyle orientalis, Exorchis oviformis, and Loxogenes liberum were found. The most frequently liberated cercaria was L. liberum 43.3 per cent, followed by E. oviformis 6.2 per cent and C. orientalis 1.5 per cent. The least frequently liberated was C. sinensis 0.1 per cent. In the monthly liberation rates for larval trematodes, the higher rates were observed in June, July and August every year, and the cercarial rates for Clonorchis sinensis, Cyathocotyle orientails and Exorchis oviformis demonstrate a fairly consistently fluctuating downward trend over the five-year period, except for Loxogenes liberum. Summarizing the results, this study indicated that the population density of snails in the habitat and the infection of the snail with the cercariae of digenetic trematodes has decreased over the five-year period from 1975 to 1979.
parasitology-helminth-trematoda ; Clonorchis sinensis ; Parafossarulus manchouricus ; Cyathocotyle orientalis ; Exorchis oviformis ; Loxogenes liberum ; epidemiology ; cercaria

A number of studies on the papillae of cercariae of trematodes reported that the papillar patterns (or chaetotaxy) of cercariae might be an excellent method to attain better understanding of the digenetic trematodes (Richard, 1971; Short and Cartrett, 1973; Bayssade-Dufour, 1979). The present study was aimed to determine the number, distribution pattern and structure of the sensory papillae of Metagonimus yokogawai cercariae, and to elucidate the chaetotaxy of this digenetic trematode. M. yokogawai cercariae were pipetted from a vial in which infected snails (Semisulcospira libertica) had been kept for 3 hours. The snails were collected from an endemic area of M. yokogawai, Boseong river in west-southern part of Korea. Observations of papillae were based on light microscopy of those stained with silver nitrate, and on scanning electron microscopy. The results are summarized as follows: All papillae observed were uniciliated. Cilia in anterior tip were shorter than the others in other portions. The body papillae were arranged in essentially symmetrical patterns. Total number of the papillae was 126(63 pairs) in average; anterior tip 40(20 pairs), ventral 20(10 pairs), lateral 42(21 pairs), and caudal 8(4 pairs). The chaetotaxy of M. yokogawai cercaria was; C(I) cycle (3+3C(I)V, 2+2C(I)L, 2+3C(I)D), C(II) cycle(2C(II)V, 1C(II)L, 2C(II)D), C(III) cycle (1+lC(III)V, 1C(III)L), C(IV) cycle (1C(IV)V, 1C(IV)L) in cephalic region: A(I)(lA(I)V, l+2A(I)L, 1A(I)D), A(II)(1A(II)V, 1+3A(II)L, lA(II)D), A(III) {lA(III)V, l+lA(III)L, lA(III)D) and A(IV)(lA(IV)V, 2A(IV)L) in antacetabular region: 1M(I)V and 2M(I)L in median: 1+lP(I)L, 1P(II)L, lP(II)D lP(III)L, lP(IV)L and 1P(IV)D in postacetabular region: 2-2-2-2 in caudal region.
parasitology-helminth-trematoda ; Metagonimus yokogawai ; electronmicroscopy ; Plecoglossus altivelis ; sensory papila ; cercaria

OBJECTIVETo detect the species of larval trematodes (cercariae) in Melanopsis praemorsa snails from 5 different fresh water bodies in Palestine.

METHODSA total of 1 880 Melanopsis praemorsa snails were collected from different fresh water bodies in Palestine from October, 2008 to November, 2010. Cercariae in Melanopsis praemorsa snails were obtained by lighting and crushing methods. The behavior of cercariae was observed using a dissecting microscope.

RESULTSThree different species of larval trematodes were identified from Melanopsis praemorsa snails collected only from Al-Bathan fresh water body, while snails from other water bodies were not infected. These species were microcercous cercaria, xiphidiocercaria and brevifurcate lophocercous cercaria. These cercariae called Cercaria melanopsi palestinia I, Cercaria melanopsi palestinia II and Cercaria melanopsi palestinia III have not been described before from this snail in Palestine. The infection rate of Melanopsis praemorsa collected from Al-Bathan fresh water body was 5.7%, while the overall infection rate of snails collected from all fresh water bodies was 4.3%. Details are presented on the morphology and behavior of the cercariae as well as their development within the snail.

CONCLUSIONSThese results have been recorded for the first time and these cercariae may be of medical and veterinary importance.

Clonorchiasis for which no specific therapy is available has been recognized as one of the serious public health problems in terms of waste of human productivity in Korea today and an urgent consideration must be given to its prevention and control. For past several years, the author has been finding that the infection rate of liver fluke in fish from the Kum-Ho river which has long been recognized as the world's notorious prevalent area of the disease, has been decreasing gradually. Here the author formulated the hypothesis that the decreasing of infection rate might be influenced by the common use of pesticide in plants along the river. Basing this hypothesis, the effective use of pesticide may contribute to the control of the disease by cutting the life cycle of liver fluke. To test above hypothesis, molluscicidal effect on Parafossarulus manchouricus and cercariacidal effect of various pesticides in liver fluke have been determined and the following results were obtained. In molluscicidal effect, the most potent agent in low concentration was Bayer 73 which is 3 to 70 times stronger than other pesticides. When compared with NaPCP which has been widely used for the eradication of Onchomelania, Bayer 73 shows 5 to 10 times stronger effect. The order of pesticide in molluscicidal effect was: Bayer 73, Nicotin, NaPCP, Sevin, Parathion, Copper sulfate and Lindane. In cercariacidal effect, the most potent agent was Parathion which had 2 to 5 times stronger effect than Bayer 73 or NaPCP. The order of pesticide in the cercariacidal effect was: Parathion, Bayer73, NaPCP, Lindane, Nicotin,Sevin, and Copper sulfate. By applying the common used concentration of pesticides considering the toxicity to plants, Bayer 73 is most potent in molluscicidal effect and then Nicotin, NaPCP, Copper sulfate, Sevin, Parathion and Lindane in order. In cercariacidal effect, Parathion is the most potent and NaPCP, Bayer 73, Lindane, and Copper sulfate are followed. Considering with the toxicity to human body the most safe and effective pesticides were Bayer 73, Seven, NaPCP, and Copper sulfate but among those agents, Bayer 73 and NaPCP show relatively stronger effect in both Parafossarulus manchouricus and cercaria of liver fluke.
parasitology ; helminth ; trematode ; Clonorhcis sinensis ; chemotherapy ; Parafossarulus manchouricus ; Onchomelania ; cercaria ; toxicology ; Bayer 73 ; Nicotin ; NaPCP ; Sevin ; Parathion ; Copper sulfate ; Lindane